MEMORANDUM. Corona Subdivision XP Storm Evaluation. Date: March 5, Curt Bates, City of Petaluma. David S. Smith, P.E., WEST Consultants, Inc.

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MEMORANDUM Project: Corona Subdivision XP Storm Evaluation Subject: Results Summary Date: March 5, 2013 To: Curt Bates, City of Petaluma No. C056132 EXP. 12/31/14 From: David S. Smith, P.E., WEST Consultants, Inc.

(WEST) for the City of Petaluma (the City) to evaluate the hydraulic impact of the proposed Corona Subdivision, located between Corona Road and the intersection of Andover Way and Monica Way (see

1 MEMORANDUM Project: Corona Subdivision XP Storm Evaluation Subject: Results Summary Date: March 5, 2013 To: Curt Bates, City of Petaluma No. C EXP. 12/31/14 From: David S. Smith, P.E., WEST Consultants, Inc. This memo summarizes the analysis completed by WEST Consultants, Inc. (WEST) for the City of Petaluma (the City) to evaluate the hydraulic impact of the proposed Corona Subdivision, located between Corona Road and the intersection of Andover Way and Monica Way (see Figure 1). Modeling completed by WEST for the FEMA map revision currently in process includes breakout flows from Corona Creek in the area of the proposed development. Elevating the Corona Subdivision to remove it from the 100 year floodplain will increase the water surface elevation in adjacent residential areas. Therefore, a new detention basin just upstream of Road is planned to mitigate the lost floodplain storage due to development. XP Storm version 2010 (build May 20, 2010) was used in this evaluation. The methods used to evaluate the hydraulic effects of the Corona Subdivision and the Road detention basin are described below along with tabular modeling results for the 10 year and 100 year events and a flood boundary map for the 100 year event. 1 of 7

2 March 5, 2013 Road Detention Corona Subdivision Modeling Approach Figure 1. Corona Subdivision and Road Detention Location The City s 10 year and 100 year XP Storm models that are the basis of the FEMA remapping effort were used for evaluating the Corona Subdivision (filenames 10yr_ xp and 100yr_ xp ). The following detail was added to the model(s) in the vicinity of Corona Creek (see Figure 2): 9 nodes were added in the right overbank of Corona Creek in the vicinity of the breakout at node cc_02 (Stonehenge Way, Andover Way, Mauro Pietro Drive, Sonoma Mountain Parkway, and Wellington Place): o cc2_l102 o cc2_l108 o cc2_l012 WEST Consultants, Inc. 2 of 8

3 March 5, 2013 o cc2_l120 o cc2_l1 o cc2_l1 o cc2_l1 o cc2_l1 o cc2_l170 The 8 x 12 culvert for Corona Creek at Wellington Place was added to the model (along with a weir for overtopping flows). Model nodes cc_0202 and cc_0203 were added, along with the following culvert details: o Upstream invert elevation = 27.5 o Downstream invert elevation = 27.2 o Length =.8 feet o Overtopping flow crest elevation = 36.8 o Overtopping flow weir width = 62 feet The pedestrian bridge for Corona Creek just upstream of Wellington Place was added to the model (along with a weir for overtopping flows). Model nodes cc_0207 and cc_0208 were added, along with the following bridge details: o Upstream invert elevation = o Downstream invert elevation = o Length = 10.7 feet o Overtopping flow crest elevation = 36.7 o Overtopping flow weir width = feet o The bridge opening is modeled as a user defined conduit with a table of depth, flow area, wetted perimeter, and top width. The low chord of the pedestrian bridge is modeled at a depth of 6.12 feet (corresponds to elevation 35.5), with a flow area of ft 2, wetted perimeter of 63.3 feet, and top width of 61.9 feet. WEST Consultants, Inc. 3 of 8

4 March 5, 2013 Figure 2. Corona Creek XP Model Detail The model filenames including the above detail were renamed Corona_10yr_weir473 _28.xp for the 10 year event and Corona_100yr_weir473_28.xp for the 100 year event. Both models include three scenarios: Base Scenario, Post Project Scenario, and Storage Scenario. The Base Scenario represents existing conditions with the detail described above. The Post Project Scenario is a modification to the Base Scenario with the removal of flood storage at the Corona Subdivision between model nodes cc2_l110 and cc2_l108 to account for placement of fill. The Storage Scenario is a modification to the Post Project Scenario with detention added upstream of Road at model node cc320_l010 (see Figure 3). WEST Consultants, Inc. 4 of 8

5 March 5, 2013 Road Detention Figure 3. Storage at XP Model Node cc320_l010 The dimensions of the proposed detention basin north of Road are summarized in Table 1 based on data provided by Steven J. Lafrachi and Associates, Inc. The top of the detention basin along Road is elevation 52.1 feet, NAVD based on review of the City s 2003 topography. This elevation is close to the Road elevation on the south side of the basin, and less than the natural ground elevation on the north and west sides of the basin. The bottom of the basin is modeled as elevation 45.1 feet, NAVD with side slopes of two units horizontal to one unit vertical (2H:1V). WEST Consultants, Inc. 5 of 8

6 March 5, 2013 Table 1. Elevation Area Relationship of the Proposed Road Detention Basin Elevation Depth Area ft, NGVD ft, NAVD ft, NAVD ft 2 ac The detention basin connection to Corona Creek is modeled with a 20 foot wide sharp crested weir with a crest elevation of 47.3 feet. The coefficient of discharge for the weir is a function of the weir crest height, the depth of flow over the weir, the channel velocity in Corona Creek, and the angle/shape of the weir relative to flow in Corona Creek. The coefficient of discharge for the lateral weir was calculated based on the following equation which relates the lateral weir coefficient to the normal weir coefficient 1 : C = C n * ((Fw 2 + 2)/(3 Fw 2 + 2)) 0.5 Where: C = discharge coefficient for a lateral weir C n = discharge coefficient for a normal weir = (H / p) for a sharp crested weir 2 H = measured head above the weir crest p = weir crest above invert Fw 2 = v 2 / g (y p) v = channel flow velocity at the cross section where C is being determined y = stage in channel For the 100 year event, the lateral weir coefficient is calculated to range from about 2.4 to 3.2, and for the 10 year event from about 2.2 to 2.9. An average value of 2.8 was used in the model for both events. An 18 inch culvert is included in the model to drain the detention basin, and this was modeled with a flap gate to prevent flow from Corona Creek from filling the detention 1 Hydraulic Engineering, Proceedings of the 1988 National Conference sponsored by the Hydraulics Division of ASCE, Colorado Springs, CO, August 8-12, 1988, pp Chow, V.T., Open-Channel Hydraulics, McGraw-Hill Publishing Company, 1959, p.362 WEST Consultants, Inc. 6 of 8

7 March 5, 2013 basin during the rising limb of the hydrograph. The modeled pipe is 100 feet long with a 0.1 percent slope (elevation 45.1 upstream to elevation 45 downstream). Design of the weir crest is recommended as an adjustable crest using stop logs or similar modular components at no more than half foot increments to allow for plus or minus 2 feet adjustment. This is recommended because the model is based on a calibration that did not include any stream gages along Corona Creek. In addition, the cross section geometry just upstream of Road is based on low detail USGS topography. In the future, updating the hydrologic modeling assumptions and model cross section geometry in this reach may lead to a different conclusion regarding the preferred weir crest elevation and/or the length of the weir. Results Without detention, the 100 year water surface elevation due to the Corona Subdivision would increase by a maximum of 0.41 feet in the vicinity of the project. Downstream on the Petaluma River, the peak discharge would increase by about 20 cfs and the maximum water surface elevation would increase by about 0.01 feet. Due to these increases, the Road detention area is recommended. Tabular comparisons of model results for the 10 and 100 year event are provided in Tables 2 and 3, respectively. Flood boundary results for existing conditions and project conditions (the Corona Subdivision with the Road detention basin) for the 100 year event are provided as Exhibit 1. The detention basin reduces 100 year event flooding in the vicinity of the Corona Subdivision by an average of about 0.7 feet. This reduction is the result of less flow breaking out from Corona Creek toward Stonehenge Way and Andover Way at model node CC2_L010. The lowest pad elevation of 39.4 feet NAVD is higher than the maximum water surface elevation of feet NAVD in this location, therefore the breakout flow would be essentially contained in the street and would not need to be shown on FEMA Flood Insurance Rate Maps during the Map Change processing for this project. The 100 year water surface elevation is also reduced in Corona Creek by an average of about 0.6 feet, and in the Petaluma River by an average of about 0.02 feet. The maximum 100 year water surface elevation in the Road detention basin is feet. This corresponds to a maximum depth of 4.61 feet and 2.39 feet of freeboard. For the 10 year event, the maximum water surface elevation is feet. This corresponds to a maximum depth of 2.21 feet and 4.79 feet of freeboard. WEST Consultants, Inc. 7 of 8

8 March 5, 2013 Conclusions The proposed Road detention basin size, weir elevation, and weir width described above represents a maximized detention configuration for the area upstream of Road. According to the model results, the proposed Corona Subdivision project with the Road detention basin reduces water surface elevations below existing elevations not only for the project site vicinity but also Corona Creek and the Petaluma River. WEST Consultants, Inc. 8 of 8

9 March 5, 2013 Table 2 10 year XP Storm Results for and With Project (Corona Subdivision plus Road

10 Flooding Source Corona Creek Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation Link1297 cc2_l010 cc2_l Link14 cc2_l010 CC2_L Link1871 CC2_L012 cc2_l Link1872 CC2_L012 CC2_L Link1298 cc2_l020 cc2_l Link1299 cc2_l0 cc2_l Link15 cc2_l090 cc2_l Link1870 cc2_l090 CC2_L Link1869 cc2_l100 CC2_L Link16 CC2_L108 cc2_l Link1873 CC2_L120 CC2_L Link1874 CC2_L120 CC2_L Link1876 CC2_L1 CC2_l Link1875 CC2_L1 CC2_L Link1877 CC2_l1 CC2_L cc0202l CC2_L170 cc_ cc320c cc320_l010 cc_ cc321c cc320_l010 cc_ cc320w cc320_l010 cc_ LCC1_963.1 cc_00 pr_05n lcc_00 cc_00 cc_ lcc_00 cc_00 cc_ L1166 cc_00 pr_ lcc_0070 cc_0070 cc_ lcc_0075 cc_0075 cc_ UW_ccTP070 cc_0075 cctp lcc_0080 cc_0080 cc_ L1124 cc_0080 pr_ UW_ccTP065 cc_0080 cctp lcc_0085 cc_0085 cc_ UW_ccTP0 cc_0085 cctp0 0 0 lcc_0090 cc_0090 cc_ L1123 cc_0090 pr_0590n UW_ccTP045 cc_0090 cctp lcc_0100 cc_0100 cc_ UW_ccTP0 cc_0100 cctp0 0 0 lcc_0110 cc_0110 cc_ UW_ccTP020 cc_0110 cctp lcc_01 cc_01 cc_ UW_ccTP010 cc_01 cctp lcc_01 cc_01 cc_ lcc_01 cc_01 cc_ lcc_01 cc_01 cc_ lcc_0170 cc_0170 cc_ LC1_ cc_0180 cc_ LC1_ cc_0180 cc_ LC1_ cc_0180 cc_ ccrrweir cc_0180 cc_ lcc_0190 cc_0190 cc_ lcc_0200 cc_0200 cc_ Link1868 cc_0202 cc_ lcc_ cc_0203 cc_ lcc_0203w cc_0203 cc_ lcc_0207 cc_0207 cc_ lcc_ cc_0208 cc_ lcc_0208w cc_0208 cc_ lcc_0208w2 cc_0208 cc_ lcc_0210 cc_0210 cc_ lcc_0220 cc_0220 cc_

11 Flooding Source Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lcc_02 cc_02 cc_ cc02l cc_02 cc2_l cc2r cc_02 cc2_r lcc_02 cc_02 cc_ cc02- cc_02 cc_ cc_02 cc_ cc02-l cc_02 cc2_l0 0 0 lcc_02 cc_02 cc_ lcc_0270 cc_0270 cc_ lcc_0280 cc_0280 cc_ lcc_0290 cc_0290 cc_ lcc_00 cc_00 cc_ lcc_0310 cc_0310 cc_ UW cc_0320 cc_ cc_0320 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_0370 cc_0370 cc_ lcc_0380 cc_0380 cc_ Link1317 cctp010 cctp Link1326 cctp010 cctp Link1318 cctp020 cctp Link1319 cctp0 cctp Link1338 cctp0 cctp Link1339 cctp0 cctp Link1337 cctp045 cctp Link1320 cctp0 cctp Link1334 cctp0 cctp Link1321 cctp0 cctp Link1342 cctp065 cctp Link1322 cctp070 cctp Link1333 cctp070 cctp Link1323 cctp080 cctp Link1324 cctp090 cctp Link1329 cctp090 cctp Link1325 cctp100 cctp Link1336 cctp110 cctp Link1332 cctp120 cctp Link13 cctp1 cctp Link1331 cctp1 cctp Link1335 cctp1 cctp Link13 cctp1 cctp Link1328 cctp170 cctp Link1327 cctp180 cctp Link1256 Cor-CC_10 pr_06n Link1736 Cor-CC_10 Cor-CC_ Link1255 Cor-CC_20 pr_00n Link1737 Cor-CC_20 Cor-CC_ Link1826 Cor-CC_ cc_ lpc_04 pc_04 pr_ lpc_0800 pc_0800 pc_ lpc_1525 pc_1525 pc_ lpr_0020 pr_0020 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_

12 Flooding Source Petaluma River Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lpr_0070 pr_0070 pr_ lpr_0080 pr_0080 pr_ lpr_0090 pr_0090 pr_ lpr_0100 pr_0094 pr_ Link12 pr_0096 pr_ Link1229 pr_0098 pr_ Link1228 pr_0100 pr_ lpr_0110 pr_0110 pr_ lpr_0120 pr_0120 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_0170 pr_0170 pr_ lpr_0180 pr_0180 pr_ lpr_0190 pr_0190 pr_ lpr_0195 pr_0195 pr_ lpr_0200 pr_0200 pr_ Link1239 pr_0206 pr_ lpr_0208 pr_0208 pr_ lpr_0210 pr_0210 pr_ lpr_0220 pr_0220 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_0270 pr_0270 pr_ lpr_0280 pr_0280 pr_ lpr_0290 pr_0290 pr_ lpr_0298 pr_0298 pr_ lpr_00 pr_00 pr_ lpr_08 pr_08 pr_ lpr_0310 pr_0310 pr_ lpr_0320 pr_0320 pr_ lpr_03 pr_03 pr_ lpr_0338 pr_0338 pr_ lpr_03 pr_03 pr_ lpr_03 pr_03 pr_ lpr_03 pr_03 pr_ lpr_0370 pr_0370 pr_ lpr_0380 pr_0380 pr_ lpr_0390 pr_0390 pr_ lpr_00 pr_00 pr_ lpr_0420 pr_0420 pr_ lpr_04 pr_04 pr_ lpr_04 pr_04 pr_ lpr_0445 pr_0445 pr_ lpr_0448 pr_0448 pr_ lpr_04 pr_04 pr_ lpr_0452 pr_0452 pr_ lpr_0458 pr_0458 pr_ lpr_04 pr_04 pr_ lpr_0465 pr_0465 pr_ lpr_0470 pr_0470 pr_ lpr_0480 pr_0480 pr_ lpr_0490 pr_0490 pr_ lpr_0496 pr_0496 pr_ lpr_0498 pr_0498 pr_ lpr_00 pr_00 pr_

13 Flooding Source Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lpr_0510 pr_0510 pr_ lpr_0520 pr_0520 pr_ lpr_05 pr_05n pr_ lpr_05 pr_05n pr_05n lpr_05 pr_05 pr_05n lpr_0552 pr_0552 pr_ pr_0554 pr_ pr_0554 pr_ lpr_05 pr_05 pr_ lpr_0570 pr_0570 pr_ lpr_0580 pr_0580 pr_ lpr_0590 pr_0590n pr_ lpr_00 pr_00n pr_0590n lpr_06 pr_06n pr_00n UWCorona pr_07n pr_06n pr_07n pr_06n lpr_08 pr_08n pr_07n lpr_0610 pr_0610n pr_08n lpr_0612 pr_0612n pr_0610n lpr_0614 pr_0614n pr_0612n lpr_0616 pr_0616n pr_0614n lpr_0618 pr_0618n pr_0616n lpr_0620 pr_0620n pr_0618n lpr_06 pr_06n pr_0620n lpr_06 pr_06n pr_06n lpr_06 pr_06 pr_06n lpr_06 pr_06 pr_ lpr_0670 pr_0670n pr_ lpr_0680 pr_0680n pr_0670n lob pr_0682 pr_0680n pr_0682 pr_0680n lob pr_0684 pr_ pr_0684 pr_ lpr_0690 pr_0690n pr_ lpr_0700 pr_0700 pr_0690n lpr_0710 pr_0710 pr_ lpr_0720 pr_0720 pr_ lpr_0723 pr_0723 pr_ pr_0725 pr_ pr_0725 pr_ lpr_07 pr_07 pr_ lpr_07 pr_07 pr_ pr_0745 pr_ pr_0745 pr_ lpr_07 pr_07 pr_ lpr_07 pr_07 pr_ Notes: (1) Change due to project--negative values indicate a decrease, and positive values an increase. Differences in discharge less than 1 cfs and water surface elevation less than 0.01 feet are left blank. Legend: = removed for project conditions (storage in empty field) = added for project conditions (detention basin)

14 March 5, 2013 Table year XP Storm Results for and With Project (Corona Subdivision plus Road

15 Flooding Source Corona Creek Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation Link1297 cc2_l010 cc2_l Link14 cc2_l010 CC2_L Link1871 CC2_L012 cc2_l Link1872 CC2_L012 CC2_L Link1298 cc2_l020 cc2_l Link1299 cc2_l0 cc2_l Link15 cc2_l090 cc2_l Link1870 cc2_l090 CC2_L Link1869 cc2_l100 CC2_L Link16 CC2_L108 cc2_l Link1873 CC2_L120 CC2_L Link1874 CC2_L120 CC2_L Link1876 CC2_L1 CC2_l Link1875 CC2_L1 CC2_L Link1877 CC2_l1 CC2_L cc0202l CC2_L170 cc_ cc320c cc320_l010 cc_ cc321c cc320_l010 cc_ cc320w cc320_l010 cc_ LCC1_963.1 cc_00 pr_05n lcc_00 cc_00 cc_ lcc_00 cc_00 cc_ L1166 cc_00 pr_ lcc_0070 cc_0070 cc_ lcc_0075 cc_0075 cc_ UW_ccTP070 cc_0075 cctp lcc_0080 cc_0080 cc_ L1124 cc_0080 pr_ UW_ccTP065 cc_0080 cctp lcc_0085 cc_0085 cc_ UW_ccTP0 cc_0085 cctp lcc_0090 cc_0090 cc_ L1123 cc_0090 pr_0590n UW_ccTP045 cc_0090 cctp lcc_0100 cc_0100 cc_ UW_ccTP0 cc_0100 cctp lcc_0110 cc_0110 cc_ UW_ccTP020 cc_0110 cctp lcc_01 cc_01 cc_ UW_ccTP010 cc_01 cctp lcc_01 cc_01 cc_ lcc_01 cc_01 cc_ lcc_01 cc_01 cc_ lcc_0170 cc_0170 cc_ LC1_ cc_0180 cc_ LC1_ cc_0180 cc_ LC1_ cc_0180 cc_ ccrrweir cc_0180 cc_ lcc_0190 cc_0190 cc_ lcc_0200 cc_0200 cc_ Link1868 cc_0202 cc_ lcc_ cc_0203 cc_ lcc_0203w cc_0203 cc_ lcc_0207 cc_0207 cc_ lcc_ cc_0208 cc_ lcc_0208w cc_0208 cc_ lcc_0208w2 cc_0208 cc_ lcc_0210 cc_0210 cc_ lcc_0220 cc_0220 cc_

16 Flooding Source Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lcc_02 cc_02 cc_ cc02l cc_02 cc2_l cc2r cc_02 cc2_r lcc_02 cc_02 cc_ cc02- cc_02 cc_ cc_02 cc_ cc02-l cc_02 cc2_l lcc_02 cc_02 cc_ lcc_0270 cc_0270 cc_ lcc_0280 cc_0280 cc_ lcc_0290 cc_0290 cc_ lcc_00 cc_00 cc_ lcc_0310 cc_0310 cc_ UW cc_0320 cc_ cc_0320 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_03 cc_03 cc_ lcc_0370 cc_0370 cc_ lcc_0380 cc_0380 cc_ Link1317 cctp010 cctp Link1326 cctp010 cctp Link1318 cctp020 cctp Link1319 cctp0 cctp Link1338 cctp0 cctp Link1339 cctp0 cctp Link1337 cctp045 cctp Link1320 cctp0 cctp Link1334 cctp0 cctp Link1321 cctp0 cctp Link1342 cctp065 cctp Link1322 cctp070 cctp Link1333 cctp070 cctp Link1323 cctp080 cctp Link1324 cctp090 cctp Link1329 cctp090 cctp Link1325 cctp100 cctp Link1336 cctp110 cctp Link1332 cctp120 cctp Link13 cctp1 cctp Link1331 cctp1 cctp Link1335 cctp1 cctp Link13 cctp1 cctp Link1328 cctp170 cctp Link1327 cctp180 cctp Link1256 Cor-CC_10 pr_06n Link1736 Cor-CC_10 Cor-CC_ Link1255 Cor-CC_20 pr_00n Link1737 Cor-CC_20 Cor-CC_ Link1826 Cor-CC_ cc_ lpc_04 pc_04 pr_ lpc_0800 pc_0800 pc_ lpc_1525 pc_1525 pc_ lpr_0020 pr_0020 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_ lpr_00 pr_00 pr_

17 Flooding Source Petaluma River Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lpr_0070 pr_0070 pr_ lpr_0080 pr_0080 pr_ lpr_0090 pr_0090 pr_ lpr_0100 pr_0094 pr_ Link12 pr_0096 pr_ Link1229 pr_0098 pr_ Link1228 pr_0100 pr_ lpr_0110 pr_0110 pr_ lpr_0120 pr_0120 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_01 pr_01 pr_ lpr_0170 pr_0170 pr_ lpr_0180 pr_0180 pr_ lpr_0190 pr_0190 pr_ lpr_0195 pr_0195 pr_ lpr_0200 pr_0200 pr_ Link1239 pr_0206 pr_ lpr_0208 pr_0208 pr_ lpr_0210 pr_0210 pr_ lpr_0220 pr_0220 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_02 pr_02 pr_ lpr_0270 pr_0270 pr_ lpr_0280 pr_0280 pr_ lpr_0290 pr_0290 pr_ lpr_0298 pr_0298 pr_ lpr_00 pr_00 pr_ lpr_08 pr_08 pr_ lpr_0310 pr_0310 pr_ lpr_0320 pr_0320 pr_ lpr_03 pr_03 pr_ lpr_0338 pr_0338 pr_ lpr_03 pr_03 pr_ lpr_03 pr_03 pr_ lpr_03 pr_03 pr_ lpr_0370 pr_0370 pr_ lpr_0380 pr_0380 pr_ lpr_0390 pr_0390 pr_ lpr_00 pr_00 pr_ lpr_0420 pr_0420 pr_ lpr_04 pr_04 pr_ lpr_04 pr_04 pr_ lpr_0445 pr_0445 pr_ lpr_0448 pr_0448 pr_ lpr_04 pr_04 pr_ lpr_0452 pr_0452 pr_ lpr_0458 pr_0458 pr_ lpr_04 pr_04 pr_ lpr_0465 pr_0465 pr_ lpr_0470 pr_0470 pr_ lpr_0480 pr_0480 pr_ lpr_0490 pr_0490 pr_ lpr_0496 pr_0496 pr_ lpr_0498 pr_0498 pr_ lpr_00 pr_00 pr_

18 Flooding Source Link ID U/S Node D/S Node Peak Discharge (cfs) U/S Node Water Surface Elevation lpr_0510 pr_0510 pr_ lpr_0520 pr_0520 pr_ lpr_05 pr_05n pr_ lpr_05 pr_05n pr_05n lpr_05 pr_05 pr_05n lpr_0552 pr_0552 pr_ pr_0554 pr_ pr_0554 pr_ lpr_05 pr_05 pr_ lpr_0570 pr_0570 pr_ lpr_0580 pr_0580 pr_ lpr_0590 pr_0590n pr_ lpr_00 pr_00n pr_0590n lpr_06 pr_06n pr_00n UWCorona pr_07n pr_06n pr_07n pr_06n lpr_08 pr_08n pr_07n lpr_0610 pr_0610n pr_08n lpr_0612 pr_0612n pr_0610n lpr_0614 pr_0614n pr_0612n lpr_0616 pr_0616n pr_0614n lpr_0618 pr_0618n pr_0616n lpr_0620 pr_0620n pr_0618n lpr_06 pr_06n pr_0620n lpr_06 pr_06n pr_06n lpr_06 pr_06 pr_06n lpr_06 pr_06 pr_ lpr_0670 pr_0670n pr_ lpr_0680 pr_0680n pr_0670n lob pr_0682 pr_0680n pr_0682 pr_0680n lob pr_0684 pr_ pr_0684 pr_ lpr_0690 pr_0690n pr_ lpr_0700 pr_0700 pr_0690n lpr_0710 pr_0710 pr_ lpr_0720 pr_0720 pr_ lpr_0723 pr_0723 pr_ pr_0725 pr_ pr_0725 pr_ lpr_07 pr_07 pr_ lpr_07 pr_07 pr_ pr_0745 pr_ pr_0745 pr_ lpr_07 pr_07 pr_ lpr_07 pr_07 pr_ Notes: (1) Change due to project--negative values indicate a decrease, and positive values an increase. Differences in discharge less than 1 cfs and water surface elevation less than 0.01 feet are left blank. Legend: = removed for project conditions (storage in empty field) = added for project conditions (detention basin)

19 March 5, 2013 Exhibit 1 Flood Boundary Comparison Map for 100 year Storm in vicinity of Corona Creek

90 70 110 cc_03 cc_03 nn ha ac ro n Co ee k Cr Co ro na 80 cc_0320 cc_0310 N.

20 cc_03 cc_03 nn ha ac ro n Co ee k Cr Co ro na 80 cc_0320 cc_0310 N. cc_03 cc_03 el Reisling Road Detention cc_00 cc02_l0 cc02_l070 cc02_l0 N OW SH T NO AI N PL EK RE IC PR CA CaC_R52 Parcels Buildings City Limits Proposed Detention Basin Project - Corona Subdivision and Detention CaC_R1 CaC_R2 0 µ Corona Subdivision and Proposed Condition Flood Boundary Comparison CaC_R1 CaC_TP80 CaC_R190 CaC_R foot Contours CaC_R110 CaC_TP70CaC_R1 cc_00 cc_0020 XP-SWMM Nodes pr_05 Stream Centerlines CaC_R76 CaC_TP CaC_TP cc_00 1 FL 4 O O0 D 20 pr_0570 CaC_0047 CaC_R54 Legend 20 CaC_TP pr_0580 CaC_R90 CaC_L120CaC_L04 CaC_R80 CaC_L1 CaC_L02 CaC_R20 CaC_L1 CaC_0584 CaC_R CaC_R70 CaC_L1 CaC_TP10 CaC_L1 CaC_R72 CaC_R CaC_L170 CaC_03CaC_R100 CaC_R74 CaC_TP20 cc_00 CaC_R94 CaC_R92 TE : cc_00 CaC_R96 CaC_L110 CaC_L CaC_L CaC_L CaC_L cc_0070 CaC_L70 cctp080 CaC_L CaC_L80 cc_0075 CaC_L90 cctp1 cctp070 cctp100 cctp090 cctp cctp1 70 cctp170 cc_0080 cctp110 cctp065 pr_0590 CaC_28 cctp0 cctp180 cctp1 cctp0 cc_0085 cc_0090 CaC_36 CaC_32 cctp1 cctp CaC_3898 McDow85 McDow83 cc_0100 cctp0 CaC_4446 McDow82 McDow86 pr_00 cc_0202 McDow81 cc_0110 cctp020 CaC_4448 CaC_3900 Cor-CC_ CaC_44 cctp010 CaC_44 CaC_4848 CaC_4846 McDow80 Cor-CC_10 cc_01 cc_01 cc_01 cc_01 70 NO cc_0170 Holm_55 cc2_r CaC_48 cc2_r cc_0190 McDow56 Holm cc2_r10 cc_0200 McDow70 McDow54 McDow58 cc02_l170 cc2_r cc2_r20 McDow48 cc_02 cc_0208cc_0207 McDowMcDow62 McDow45 CaC_5171 cc_0220 McDow cc02_l012 cc02_l120 cc02_l010 cc02_l1 McDow46 RR78 cc_02 cc02_l1 cc02_l1 RR80 cc02_l0 cc_02 cc02_l020 RR76 RR90 cc_02 Corona Subdivision McDow42 cc02_l0 RR74 RR70 cc02_l080cc_ cc_ cc_ Feet Vertical Datum = NAVD 1988 February 2013

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